a. Field of the Invention
The present invention concerns a lighting system, and in particular, a lighting system for use with a machine vision system for inspecting parts.
b. Related Art
Machine vision is becoming an integral part of automation. Manual inspection of part attributes, is becoming impractical, even at low manufacturing output levels. This is because manual part inspection is subjective, time consuming, and expensive. Automated inspection systems employing machine vision overcome many of the drawbacks of manual part inspection.
However, to optimize machine vision inspection systems, the part being inspected must be properly lit. Strobe lights are often used as light sources for machine vision inspection system. When such strobe lights are properly installed and controlled, illumination of the part being inspected is optimized such that an image capturing means of the machine vision inspection system may capture a good, clean image of the part. Further, different parts, or different sections of a particular part, may require different lighting (e.g., back lighting, ring lighting, strobe lighting, etc.) such that an optimal image is captured. Moreover, it may be necessary to capture multiple images of a particular part.
Basically, known systems adapt to changing lighting conditions in one of three ways; namely (i) controlling the intensity of a light source, (ii) controlling light rays propagating towards an image capturing means, or (iii) adjusting a thresholding level applied to a captured image.
For example, U.S. Pat. No. 4,855,830 ("the Davis patent") discusses a method in which the effects of changes in the light level are compensated for by (i) measuring the luminance of a captured image, (ii) setting a threshold As based on the measured luminance, and (iii) processing the image using the threshold. Similarly, U.S. Pat. No. 5,311,598 ("the Bose et al patent") adjusts a threshold based on pixel intensity of a captured image. Unfortunately, the methods discussed in these patents are limited to the manner in which a captured image is processed. The image initially captured is not improved by these methods.
U.S. Pat. No. 5,305,012 ("the Faris patent") discusses an electro-optical system having an optical surface formed from addressable pixels having controllable light transmitting characteristics. The light transmitting characteristics of certain pixels are modulated to modulate the intensity of light rays propagating through the electro-optical system towards an image capturing means. Unfortunately, this system is relatively complex, and yet does not improve the quality of the light initially reflected from the image.
Lastly, U.S. Pat. No. 5,078,496 ("the Parker et al patent") discusses a surface quality detection system in which the light intensity of a light source is controlled to maintain substantially constant light intensity. This is done by controlling the light exposure with a shutter or by pulsing the light based on the output of a photoresistor such that the light intensity is controlled in a closed loop. Unfortunately, this control of the light source is relatively simple and is not easily adaptable for optimally lighting different parts or different areas of a given part.
To maximize the use of a machine vision inspection system, the system should be adaptable for inspecting a number of different parts and a number of different features of a given part. However, the different parts and different features of a given part will often require different types of lighting to provide a good, clean image to the image capturing means of the machine vision inspection system. Thus, a flexible, easily configurable lighting system is needed.